1. Technical Field
The present invention relates to a laser device comprising a laser light source that generate a laser light in a pulse waveform, an intensity modulator which extracts and emits the laser light which is outputted from the laser light source, an amplifier which amplifies the laser light which is emitted from the intensity modulator, and a wavelength conversion optical element which converts the wavelength of the laser light which is amplified by the amplifier. The present invention also relates to a system, such as an exposure device or an inspection device, provided with such a laser device.
2. Description of Related Art
The laser device as mentioned above is used, for instance, as a light source for laser systems such as a microscope, a shape measurement device, an exposure device, and an inspection device. The output wavelength of the laser device is set according to the usage and function of a system in which the laser device is installed. For instance, a laser device which outputs a pulse light having a wavelength of 193 nm, a laser device which outputs a pulse light having a wavelength of 355 nm, etc. are known. The wavelength of a laser light generated from the laser light source, the number of rows and the number of stages of the amplifier, the types and combinations of wavelength conversion optical elements provided in the wavelength conversion unit are set according to the usage and function of the laser system (see Japanese Laid-Open Patent Publication No. 2004-86193).
An example of such a laser device as mentioned above is known, which includes, as means for turning on/off the light (ultraviolet light) which is outputted from the laser device, a construction which changes the pulse waveform of the laser light which enters an amplifier based on high and low efficiencies of wavelength conversion in the wavelength conversion optical element. For instance as shown in FIG. 13, if it is desired to turn on the output light, a first laser light in a pulse waveform having a relatively short pulse duration and a high peak power (hereafter, referred to as “first pulse light”) Ls1 is outputted from a laser light source 910 at a predetermined period, whereas if it is desired to turn off the ultraviolet light, a second laser light in a pulse waveform having a relatively long pulse duration and a relatively low peak power (hereafter, referred to as “second pulse light”) Ls2 is outputted from the laser light source 910 at the same period as above.
The first pulse light Ls1 and the second pulse light Ls2 have different pulse durations and different peak powers from each other. However, they have substantially the same energy of light pulse energy (average power per unit time). The second pulse light Ls2 is output at the predetermined frequency also in case it is desired to turn off the output light to keep constant an inverted distribution state of the amplifier. In addition to the above-mentioned construction, in which the state of light emission of the laser light source 910 is directly modulated, a technology has been proposed, in which an intensity modulator is provided between the laser light source and the amplifier to enable a portion of the laser light which is outputted from the laser light source to be extracted by the intensity modulator so that a first pulse light Ls1 and a second pulse light Ls2 are outputted (see refer Japanese Patent No. 4517271).